1. Field of the Invention
The present invention relates to a circuit board for peripheral circuits of high-capacity modules. More particularly, the present invention relates to a circuit board for peripheral circuits to be laminated with a circuit containing a high exothermic element in high-capacity modules including power modules, such as an inverter used in a hybrid car or an electric vehicle, etc. Furthermore, the present invention also relates to a high-capacity module including a peripheral circuit which uses the circuit board.
2. Description of Related Art
Conventionally, in high-capacity (large electric power) modules including power modules, such as an inverter, a circuit containing a power semiconductor element, such as a switching element (for example, IGBT (Insulated Gate Bipolar Transistor)) (may be referred to as a “power circuit” henceforth) and a peripheral circuit which controls such a power semiconductor element (may be referred to as a “drive circuit” henceforth) are arranged planarly, and the area for arranging the wiring (wire) for connecting these circuits is required, and these have become a factor for preventing reduction in size and weight of a high-capacity module (for example, refer to FIG. 2).
In the present specification, a high-capacity module refers to a module handling a large electric power with a voltage of 200V or more or a current of 10 A or more. As a specific example of such a high-capacity module, for example, what is called a “power module” etc. can be exemplified.
Moreover, concerns that wiring length becomes longer due to the wiring for connecting various circuits which constitute high-capacity modules as mentioned above, the loss as the whole module becomes larger, and the surge voltage which generates on switching due to the equivalent inductance of the wire becomes larger have been recognized. Excessive surge voltage has a possibility of damaging, for example, a semiconductor element in a drive circuit, etc.
By the way, in recent years, for example, along with the popularization of hybrid vehicles and of electric vehicles etc., further improvement in performance such as reduction in size and weight, reduction in surge (surge control), and higher-efficiency (reduction in a loss), etc. has been increasingly demanded.
Then, approaches to laminate circuit boards for various circuits which constitute high-capacity modules as mentioned above in order to attain reduction in size and weight of the high-capacity modules and to improve the connection configuration between the various circuit boards which constitute the high-capacity modules in order to attain reduction in surge and reduction in a loss have been proposed (for example, refer to Patent documents 1 to 3).
However, when various circuit boards which constitute a high-capacity module are laminated as mentioned above, reduction in size and weight of the module can be attained, while it may become more difficult to transmit and release heat which generates from a power semiconductor element, such as a switching element and, therefore, there is a possibility that a problem, such as breakage of the module (for example, degradation of sealing resin of a circuit element which constitutes the module) etc. may occur.
In the present specification, a high exothermic element refers to an element whose temperature may reach 120° C. or higher in its operating state. As a specific example of such a high exothermic element, for example, a power semiconductor element etc. can be exemplified. Moreover, as a specific example of such a power semiconductor element, for example, a switching element etc. can be exemplified. Furthermore, as a specific example of such a switching element, for example, an IGBT as mentioned above, an SiC-MOSFET which will be mentioned later, etc. can be exemplified.
To problems as mentioned above, an approach to stick a leadframe to an undersurface of a circuit board of a drive circuit laminated on a power circuit containing a switching element and thereby release heat generated from the switching element in a direction toward an upper surface (upper direction) of a module through the leadframe while reducing a switching loss and switching surge has been also proposed (for example, refer to Patent Literature 1 (PTL 1)). However, in such a configuration, since the pathway to the upper direction of the heat generating from the switching element is limited to the leadframe, there is a possibility that the heat dissipation effect may become insufficient.
Moreover, when a resin circuit board is used in a drive circuit laminated with a power circuit, there is a possibility that, due to heat generation from the power circuit, the resin circuit board may expand and/or deform and it may lead to decrease in reliability and/or lead to disconnection or destruction of the circuit at worst.
On the other hand, as a loss remedy of a power semiconductor element including IGBT, MOSFET, etc., it has been proposed to use a silicon carbide (SiC) wafer in place of a silicon (Si) wafer which has been used conventionally. This SiC wafer has a feature that an operation at higher temperature is possible, as compared with a conventional Si wafer. Thereby, a cooling mechanism (for example, a heat sink, a water-cooling mechanism, etc.) which has been indispensable in a power module which uses a conventional Si wafer can be drastically simplified. As a result, reduction in size and weight of a power module can be also attained by using a SiC wafer. However, there is a tendency that various problems due to heat generation from a high exothermic element as mentioned above become still severer by a rise of an operation temperature of the power module accompanying use of a SiC wafer.
Moreover, since thickness of a conductor used in a peripheral circuit is thin, there is also a subject that the loss at the time of passing current is large.